The invention relates to a method for the releasing of an insert from the shell of an artificial joint pan as well as to an artificial joint pan.
Artificial joint pans in general, but in particular however hip joint pans, which are implanted into the acetabulum of a patient, comprise as a rule the following essential parts: A shell on the one side which is mainly manufactured of titanium or of a titanium alloy in the case of cement-free implantation (in cemented implantation e.g. of a cobalt-chromium alloy) and an insert on the other side which can be placed into this shell and which is as a rule manufactured either of polyethylene or ceramic or is metallic. The insert has a joint surface on which the joint ball, in a hip joint pan the femur-side joint ball, is movable. During the implantation of an artificial hip joint pan of this kind the shell is typically first secured in the acetabulumxe2x80x94numerous kinds of securing are known for this. After the securing of the shell the insert is introduced into the shell, and indeed in such a manner that it is arranged in a fixed manner in the shell after the introduction.
The arranging in the shell in a fixed manner can take place in different ways: For inserts of polyethylene this can for example take place in that the insert (also called an xe2x80x9cinlayxe2x80x9d) snaps in through a snap connection into the shell, thus in that two mutually undercutting parts slide past one another and in this way enter into a snap connection which cannot be released without special measures.
In the case of harder materials of the inserts such as ceramic or metal, cone connections are being used for some time now in which the fixed connection comes about with the help of a conical surface on the outer wall of the insert and a corresponding conical surface on the inner wall of the shell. The insert of ceramic or of metal respectively is held firmly in a clamping seat in the shell which cannot be released without special measures.
Even though joint pans of this kind are very durable and can also stand high stresses, it can however become necessary for various reasons to subject an artificial pan of this kind to a revision after some time. In this case one naturally does not wish to renew the entire joint pan, but merely the insert, because the shell is as a rule firmly and well connected to the bone material of the acetabulum. On the other hand however the insert is firmly connected to the shell and cannot simply be released from the shell without further ado.
In inserts of polyethylene (snap connection between the insert and the shell) the releasing of the insert from the shellxe2x80x94in the above-explained example thus the releasing of the snap connectionxe2x80x94takes place for example in such a manner that an auxiliary tool is screwed through the polyethylene insert in accordance with the principle of the corkscrew. The front end of the auxiliary tool braces itself against the (titanium) shell when screwed further in and forces the insert out of the shell in that the mutually undercutting parts of the insert and the shell again slide past one another (against the restraining force of the snap connection), but this time however in the direction opposite to the insertion, through which the snap connection is released.
In inserts of harder materials such as ceramic or metal, which are firmly arranged in the shell via a cone clamping seat, other methods must be used. A known method for the releasing of a cone clamping seat of this kind consists in transmitting a striking impulse (for example using a suitable auxiliary tool) to the shellxe2x80x94but not to the insert howeverxe2x80x94through which the cone clamping seat is released.
It is immediately evident that both measures are not exactly convenient for the surgeon or orthopedist respectively who performs the operation. The screwing in of the auxiliary tool in polyethylene inserts is comparatively difficult. The releasing of ceramic or metal inserts by means of a striking impulse is likewise somewhat difficult because a corresponding auxiliary tool for the transmission of the striking impulse must first be applied to the pan and secured against a slipping off, and only then can the striking impulse be produced. Moreover, this procedure is such that the transmission of the striking impulse can have a negative effect on the bone matter. Moreover, it is also not ensured whether inserts which were inserted in the shell over a number of years ago in the body of a patient can reliably be released through the transmission of a striking impulse to the shell.
An object of the invention is thus to propose a simple and at the same time gentle and reliable method for the releasing of the insert from the shell which is suitable both for the releasing of inserts of polyethylene and for the releasing of inserts of harder materials such as ceramic or plastic. Furthermore, it is an object of the invention to propose a corresponding artificial joint pan.
This object is satisfied by introducing a fluid between the insert and the shell when releasing the insert from the shell, which facilitates the releasing of the insert from the shell. This is comparatively simple, as shall be explained more precisely, and also takes place without a stress for the surrounding bone tissue in which the shell is anchored. After the releasing of the insert, the insert can simply be removed from the shell and a new insert can be introduced into the shell.
A liquid, in particular a body compatible liquid, is preferably used as the fluid. This can for example be a body compatible cooking salt solution. In principle it is also possible to use a gas as the fluid; due to the incompressibility of liquids, however, a preference will be given to a liquid in the majority of cases.
Especially in the case of inserts of harder materials such as ceramic or metal it is regularly the case that when the insert is firmly introduced into the shell an intermediate space is still present between the base of the shell and the base of the insert. As a result of this, in one exemplary embodiment the fluid or the liquid respectively is introduced into this space between the base of the shell and the base of the insert until the insert is released from the pan, that is, the cone clamping seat is released. After the releasing of the insert from the shell the insert can then simply be removed from the shell and a new insert introduced.
In inserts of polyethylene the connection of the insert and the shell frequently consists in a snap connection near the base of the insert. The base of the insert of polyethylene rests more or less on the base of the shell, for which reasonxe2x80x94in contrast to inserts of harder materials such as ceramic or metalxe2x80x94practically no space is present between the base of the shell and the base of the insert into which the fluid or the liquid can be introduced. For this reason a groove which is upwardly open, e.g. a ring groove, can be provided in the shell into which the fluid or the liquid respectively can be introduced. Through the fluid or the liquid respectively which is introduced into this groove (under pressure) the insert can be pressed out of the shell until the snap connection is released. After the releasing of the snap connection the insert can be removed from the shell in a simple manner.
In general it can thus be stated that in this variant the fluid or the liquid respectively is introduced into a space which extends beneath the base of the insert. This canxe2x80x94as described abovexe2x80x94either be a space which extends between the base of the shell and the base of the insert (e.g. a cone clamping seat in inserts of harder materials) or an upwardly open groove which is provided in the shell, e.g. the named ring groove (e.g. in inserts of polyethylene resting on the base of the shell).
The fluid or the liquid respectively can also be introduced into a space between the side wall of the shell and the side wall of the insert, which is interesting in particular in the case of inserts of harder material such as ceramic or metal. This measure can take place either alone or in addition to the introduction of the fluid into the space between the base of the shell and the base of the insert.